private void markOnlyTopUnit() {
if (units.size() > 0) {
if (quadMap.getGameData() != null) {
Group group = quadMap.getActiveGroup();
UnmarkAllUnits unmarkAllUnits = new UnmarkAllUnits(group,
quadMap.getGameData());
unmarkAllUnits.execute();
MarkUnit markUnit = new MarkUnit(group, units.get(0));
markUnit.execute();
} else {
Messages.getMessages().info("QuadIsoLayUnitView", "QMapWarn",